By Rick Riordan
Rick Riordan does Egyptian mythology: a brother and sister discover they carry the blood of the pharaohs after their father releases five gods, and one of them, the god of chaos, wants to destroy the world.
Carter and Sadie Kane barely know each other, one raised traveling with their Egyptologist father, the other in London with their grandparents. On Christmas Eve their father takes them to the British Museum, blows apart the Rosetta Stone, and vanishes, unleashing five Egyptian gods. The worst of them is Set, the god of chaos, who traps their father and plans to level North America. The children learn they're descended from pharaohs and can channel the power of the gods themselves, and they race across the world, magic waking up inside them, to stop Set before their father is lost for good.
For a child nearly ready for Percy Jackson, this is Riordan at full strength in a different mythology, so it stretches them without leaving the world they're building toward. The voice is the same fast, funny first-person the Percy books run on, the two-narrator setup keeps it lively, and the peril and stakes sit right at the level of the real Lightning Thief. It's also the longest, densest book so far on the trail, which subtly grows the stamina they'll need for the novel at the top. And it opens its own trilogy, plus a whole crossover universe with Percy, if it takes.